Silver: Rasmussen polls ‘biased'; How did pollsters do here?

New York Times polling guru Nate Silver has done a quick analysis of how pollsters fared this election and has declared Rasmussen Reports the big loser.

Rasmussen’s polls were quite biased, overestimating the standing of the Republican candidate by almost 4 points on average. In just 12 cases, Rasmussen’s polls overestimated the margin for the Democrat by 3 or more points. But it did so for the Republican candidate in 55 cases — that is, in more than half of the polls that it issued.

Which pollsters performed well in the closely-watched Washington Senate election?

Right now Patty Murray’s margin of victory is 2.52 percentage points. That’ll change, as there are tens of thousands of votes yet to be counted, but it’s looking like Murray will win by between 2 and 3 percentage points.

In the polls conducted in the weeks before the election, FOX had Murray up by 2, the Washington Poll had Murray up by 4, YouGov/Polimetrix had the Democrat ahead by 3 and Marist/McClatchy had Murray with a 1 point advantage.

Rasmussen’s last sampling had Rossi up by 1, but 10 days before showed Murray ahead by 3. The last poll released before the Nov. 2 election was by Public Policy Polling, which had Rossi up by 2. SurveyUSA’s last sampling had the candidates tied.

Polling’s a tricky business. Most surveys have a margin of error between about 2.5 and 4.5 percent. That’s important to keep in mind. What that means is a candidate who is up by 2 but within the margin of error is essentially tied, as far as the pollsters are concerned.

Rasmussen, which has been criticized before for leaning toward GOP candidates, took 14 polls this year in the Washington Senate race. Seven showed the Democrat ahead, six favored the Republican and one had the candidates tied.

As a keen consumer of polls, I generally think the various outfits did OK. Taken as a whole, the surveys showed a close race but generally indicated that Murray was slightly ahead. The actual results proved that to be the case.